mine worst ones have to be when i got universe blaster his friction clip thing that held his cockpit on his arm was warped so the cockpit WOULD NOT stay on.
also my HFTD terradives WHOLE upper left leg was bent. like when the plastic was coolio when he was made it got bumped or something. won't stand rght at all.

on my HFTD Seaspray the pin hole on one of the fans was put in too low making it a little more higher than the other and a little less moveable. Yeah it's not that bad and not really that noticable but that is the worst that I have got.

Leader Sentinel had to be exchanged since one of the shoulder clips was deformed in a way that the arm didn't stay put. Very tiny defect that affected the whole toy.

TRU Masterpiece Rodimus having an ankle already broken in the box followed by the other ankle joint and the shoulder joint both crumbling to pieces. The second one I got his fine, but the first was the about the worst QC problem I've experienced not only with TFs, but with any type of product ever.